Rubiaceae, the Madder Family
Herbs or shrubs, with opposite or whorled leaves and regular flowers; sepals 4, or minute or almost wanting; petals 4, united; stamens 4; ovary inferior.
| 1a. Shrub (1-3 m. tall; flowers white, in spherical heads, summer) | Button Bush, Cephalanthus occidentalis. |
| 1b. Herbaceous — 2. | |
| 2a. Leaves opposite — 3. | |
| 2b. Leaves whorled; flowers white, green, or purple (Bedstraw) — 6. | |
| 2c. Leaves whorled; flowers yellow | Bedstraw, Galium verum. |
| 3a. Leaves about as long as wide (trailing; flowers paired, white, in spring) | Partridge Berry, Mitchella repens. |
| 3b. Leaves at least twice as long as wide — 4. | |
| 4a. Corolla salver-form, about 1 cm. wide; peduncles 1-flowered (about 1 dm. high; flowers blue or white, in spring) | Bluets, Houstonia coerulea. |
| 4b. Corolla funnel-form, about 5 mm. wide; flowers in clusters (1-2 dm. high; flowers white or pale-purple, summer) (Houstonia) — 5. | |
| 5a. Basal leaves strongly ciliate | Houstonia, Houstonia ciliolata. |
| 5b. Basal leaves smooth | Houstonia, Houstonia longifolia. |
| 6a. Leaves in whorls of 4-7. | |
| 6b. Leaves in whorls of 6-8 — 16. | |
| 7a. Ovary and fruit hispid with hooked bristles (3-7 dm. high; summer) — 8. | |
| 7b. Ovary and fruit not bristly (early summer) — 11. | |
| 8a. Leaves with 1 principal vein (flowers dull purple) | Bedstraw, Galium pilosum. |
| 8b. Leaves with 3 principal veins — 9. | |
| 9a. Flowers bright-white | Bedstraw, Galium boreale. |
| 9b. Flowers greenish, yellowish, or purplish — 10. | |
| 10a. Leaves acuminate | Bedstraw, Galium lanceolatum. |
| 10b. Leaves acute or obtuse | Bedstraw, Galium circaezans. |
| 11a. Corolla-lobes 3 (2-6 dm. high; flowers white or greenish) — 12. | |
| 11b. Corolla-lobes 4 — 13. | |
| 12a. Flowers in clusters of 2 or 3 | Bedstraw, Galium claytoni. |
| 12b. Flowers solitary in the axils, on long hair-like pedicels | Bedstraw, Galium trifidum. |
| 13a. Corolla brownish or purple (3-6 dm. high) | Bedstraw, Galium latifolium. |
| 13b. Corolla white (1-4 dm. high) — 14. | |
| 14a. Flowers rather numerous in small cymes | Bedstraw, Galium palustre. |
| 14b. Flowers in clusters of 2 or 3, or solitary — 15. | |
| 15a. Principal leaves spreading or ascending | Bedstraw, Galium tinctorium. |
| 15b. Principal leaves recurved or reflexed | Bedstraw, Galium labradoricum. |
| 16a. Ovary and fruit bristly or hispid — 17. | |
| 16b. Ovary and fruit not bristly (summer) — 18. | |
| 17a. Leaves narrowly lanceolate to linear, mostly 6-8 in a whorl (stem 5-15 dm. long; flowers white; spring and summer) | Bedstraw, Galium aparine. |
| 17b. Leaves narrowly oval or elliptical, mostly in whorls of 6; flowers in clusters of 3 (1-5 dm. high; flowers greenish, summer) | Bedstraw, Galium triflorum. |
| 18a. Leaves cuspidate or mucronate at the apex (flowers white) — 19. | |
| 18b. Leaves obtuse at the apex (flowers white or greenish; 2-6 dm. high) — 20. | |
| 19a. Flowers very numerous in terminal panicles (stem 3-8 dm. long) | Bedstraw, Galium mollugo. |
| 19b. Flowers in axillary clusters (1-3 dm. high) | Bedstraw, Galium tricorne. |
| 19c. Flowers few, in small loose terminal cymes — 20. | |
| 20a. Stem smooth or nearly so (2-4 dm. high) | Bedstraw, Galium concinnum. |
| 20b. Stem hispid with reflexed bristles (5-15 dm. long) | Bedstraw, Galium asprellum. |